Preheat the oven to 375°F (190°C). Line a baking sheet with parchment or lightly oil it.

Caramelize the onion: thinly slice the onion and cook slowly in a skillet over medium-low heat with 1–2 tablespoons oil or butter. Stir occasionally until deeply golden and sweet, about 25–30 minutes. Let cool slightly.

In a large bowl, combine ground beef, breadcrumbs, Parmesan, egg, cooled caramelized onion, garlic powder, onion powder, salt, and pepper.

Mix gently with your hands or a spoon until just combined — don’t overwork the meat.

Shape into even meatballs (about 1.5 inches / tablespoon-sized yields ~16 meatballs). Place on the prepared baking sheet.

Bake for 20–25 minutes, or until an instant-read thermometer inserted into a meatball reads 160°F (71°C).

While the meatballs bake, bring beef broth and Worcestershire sauce to a gentle simmer in a saucepan.

Transfer the baked meatballs to the simmering broth and let them steep for 4–5 minutes so they absorb extra flavor.

Move the meatballs to an oven-safe serving dish, spoon a little of the broth over them, and sprinkle evenly with shredded mozzarella.

Return to the oven for 3–6 minutes, or broil briefly, until the cheese is melted and slightly golden — watch closely under the broiler.

Garnish with chopped parsley and serve hot. Offer crusty bread to mop up the broth or set them over mashed potatoes for a fuller meal.